This invention relates generally to the production of free-standing material layers, and more particularly relates to structure and techniques for the production of a free-standing crystalline material layer after formation of that layer.
For many optical and electronic device applications, it is becoming increasingly important to produce free-standing structures, such as free-standing substrates and layers, of various semiconducting materials for which bulk substrates cannot be conventionally produced. For example, the class of group III, nitride-based semiconductors, or III-N semiconductors, are rapidly becoming the materials of choice for short wavelength light emitters as well as high-frequency, high-power electronics, but development of such electronics has been limited by the difficulty in production of large-area native III-N material substrates such as gallium nitride (GaN) substrates.
In general, in the production of substrates such as GaN substrates, a deposition process, such as an epitaxial deposition process, is employed to produce an epitaxial layer of, e.g., GaN, on a supporting, or host, substrate, which may include a growth seed layer. After growth of the epitaxial layer, the underlying host substrate is removed to produce free-standing material, e.g., a GaN layer or substrate. Complete removal of the host substrate is desirable, for example, to reduce stress in the epitaxial layer due to, for example, a difference in thermal expansion coefficient between the epitaxial layer and host substrate. Removal of the host substrate is also preferred to control the electrical conductivity of the epitaxial layer, to control the thermal conductivity of the epitaxial layer, and to control the optical properties of the epitaxial layer for a given device application. But in general, conventional host substrate removal techniques tend to cause defects or even cracks in a semiconductor epitaxial layer formed on the host substrate, and are slow and irreproducible, and therefore not cost-effective processes for incorporation into a microfabrication process sequence.